1. Field
Embodiments of the present disclosure relate to an electric disc brake, and more particularly, to an electric disc brake capable of easily controlling an actuator when a parking brake force is released and preventing a damage to a component due to an excessive releasing of the parking brake force.
2. Description of the Related Art
Generally, an electric disc brake is a device for braking a vehicle by forcibly squeezing a friction pad against both sides of a disc rotated together with a wheel of the vehicle, and for performing a parking brake function by being electrically activated to maintain a stationary state of the vehicle upon a parking thereof. Such an electric disc brake is provided with a pair of pad plates disposed at both sides of a disc and squeezing the disc to generate a brake force, a carrier supporting the pair of pad plates, a caliper housing slidably installed at the carrier so as to squeeze the pair of pad plates and having a piston moved by a brake hydraulic pressure, and an actuator actuating the piston by a mechanical mechanism.
The electric disc brake may employ a so-called ball in ramp (BIR) form including a fixing ramp plate fixedly installed inside the caliper housing, a rotating ramp plate being rotated by the actuator, a ball installed between the fixing ramp plate and the rotating ramp plate to advance the rotating ramp plate upon a rotation thereof, a pushrod for pushing the piston in contiguity with the rotating ramp plate, an adjuster screw-coupled to the pushrod, and a spring for returning the pushrod to an initial position thereof.
Such a BIR form is typically referred to as a BIR caliper type, and an electric disc brake of a BIR caliper type is disclosed in U.S. Patent Application Publication No. 2012-0292141, Korean Patent Laid-Open Publication No. 2013-0034605, and the like. According to the disclosures in these literatures, the electric disc brake is configured to generate a parking brake force by delivering a rotational force generated from a motor of an actuator to a rotating ramp plate of a ramp unit through a decelerator (a gear assembly), converting a rotational movement into a rectilinear movement to push a pushrod, and tightly squeezing a friction pad against a disc by pushing a piston by means of the pushrod together with an adjuster.
At this point, the rotating ramp plate is directly engaged with a final output gear among gears of the decelerator to receive the rotational force, thereby being rotated in a direction at which a parking brake force is applied or released.
The electric disc brake described above, however, has problems in which a precise control is required to equalize a rotation amount of the rotating ramp plate for releasing the parking brake force with that of the rotating ramp plate for generating the same, and also a separate sensor should be provided for the precise control. Consequently, a manufacture cost may be increased.
Also, when the parking brake force is released, there is a problem in which a drag phenomenon caused by a continuous contact between the disc and the friction pad due to a residual parking brake force occurs if the rotation amount of the rotating ramp plate is insufficient.
Moreover, when a rotational force is excessively delivered upon releasing the parking brake force, a ball may be escaped from a ramp unit or an excessive weight is applied to internal components to cause damage thereto.